No it doesnt:
HERE
from the galaxy scenario file
planetType
designName "WeightedNonIcePlanet"
entityDefNameCount 6
entityDefName "PlanetTerran"
entityDefName "PlanetDesert"
entityDefName "PlanetVolcanic"
entityDefName "PlanetAsteroid"
entityDefName "PlanetAsteroid"
entityDefName "PlanetDeadAsteroid"
This is the entry most used for planets in the random maps more or less. If you wanted that to be more likely a Terran planet all you have to do is copy the Terran entry 7 times...
So for example:
planetType
designName "WeightedNonIcePlanet"
entityDefNameCount 6
entityDefName "PlanetTerran"
entityDefName "PlanetTerran"
entityDefName "PlanetTerran"
entityDefName "PlanetTerran"
entityDefName "PlanetTerran"
entityDefName "PlanetTerran"
entityDefName "PlanetTerran"
entityDefName "PlanetDesert"
entityDefName "PlanetVolcanic"
entityDefName "PlanetAsteroid"
Tada, now it has a 70% chance of being a terran and 10% Volcanic, 10% Desert, 10% Asteroid.
Now you might Say "But varying the resource asteroids would need to alter code!" No it doesn't
you see there is a file for every 'planet' type. Copy the file, change the resource asteroid quantity or type in it, and rename it ... PlanetTerran002A for example. You made a new planet, you just need to add it to the above entry, each random entry will grow in size with the more variables, but its easy, just copying and pasting. Its so easy you can mod the game for this entirely with Note-Pad!
So don't tell me the game can't do it Annatar... I've already done this with a map! I did it MONTHS ago during Beta 3. No extra game logic or code. Its absurdly simple to do, and I can only assume it was done so to be gloriously convenient for mod happy people

I just don't neccessarily want to do the work on something that should be a given in any space game.
Its annoying to do but I can make the game select for a planet a 'anomaly' entry that will place either a magnetic or Ion storm, or asteroid field. A dead planet entry, that will sometimes place a Gas Giant, a planet entry that places a Volcanic, but I have 5 versions some with more militia some with less, some with more resource asteroids, some with NONE. Its all Very very Very doable Annatar.